1. Field of the Invention
The present invention relates to an analyzing method of a blood coagulation reaction. More particularly the invention relates to an analyzing method of a blood coagulation reaction for measuring a blood coagulation time, the method being capable of detecting abnormality in the blood coagulation reaction.
2. Description of Related Art
Blood coagulation detection methods include the method of detecting the increase in viscosity (viscosity detection method), the method of detecting turbidity (turbidity detection method), and their combined method.
In the viscosity detection method, a bar-shaped or spherical magnetic element is placed in the plasma specimen, and a coagulation reagent is added. The motion of the magnetic element becomes slower due to coagulation, and this slowing down is detected.
However, The viscosity detection method produces variable results depending on the shape of the fibrin clumps which are the final product of blood coagulation (that is, the quantity or viscosity of the fibrin). Furthermore, it is impossible to detect coagulation unless the viscosity increases to above a specific level. Besides, because the measurement principle is based on observing the motion of the magnetic element, it is dependent on the strength of the magnetic field of the element.
The turbidity detection method involves mixing the plasma specimen and coagulation reagent, and it does not require a magnetic element or the like. The method can be the transmitted light detection method or the scattered light detection method. With these methods of detection, if the fibrinogen quantity is small, the change in the quantity of transmitted or scattered light can be detected, and it is hence free from the shortcoming of the viscosity detection method.
Methods for analyzing a blood coagulation point include: (1) a percentage detection method; (2) a differential method; (3) a double differential method; (4) an inflection point method; (5) a fluctuation detection method and the like. Among them, in the percentage detection method, the blood coagulation point is detected as a point showing a 50% optical change amount relative to the optical change amount when the blood coagulation finishes, at which point an optical change rate per a unit time is the largest and the rate of polymerization reaction of fibrin monomers is high. Thereby more precise coagulation measurement can be performed for samples such as low fibrinogen samples, chyle samples and laked blood samples.
Normally, for analyzing a blood coagulation reaction, plasma is mixed with a blood coagulation reagent to start the blood coagulation reaction, and the degree of turbidity during the process of the plasma coagulating, that is, during the process of fibrin formation, is detected as a change of the intensity of a signal by an optical detector. If the optical detector is of a scattered light detection system, such a change is represented with time plotted in abscissa and the scattered light amount (intensity) plotted in ordinate, for example, as shown in FIG. 1.
Point A in FIG. 1 indicates a time when plasma is mixed with a coagulation reagent to start the blood coagulation reaction. Then, the blood coagulation reaction advances through a cascade reaction. As stable fobrous fibrin is formed by fibrinogen in the plasma, a change appears in the amount of scattered light (point B). As the formation of the stable fibrin advances, the amount of the scattered light increases. When most of fibrinogen is consumed, the amount of scattered light does not change any more and the blood coagulation reaction terminates (point C). Supposing that the amount of the scattered light at point B is taken as 0% (non-coagulation level) and the amount of scattered light at point C is taken as 100%, a blood coagulation time may be defined as a point where the amount of the scattered light reaches 50% (point T). ΔH is indicative of a change of the amount of scattered light from the start of the blood coagulation reaction to the termination thereof.
Typically, the following complicated process leads to the formation of fibrin. The blood coagulation progresses by two pathways in general: One pathway is called as an extrinsic pathway, through which, starting with tissue thromboplastine discharged from epidermic cells and the like, the coagulation factor VII is activated, which in turn activates the coagulation factor X, then, the activation of the coagulation factor V and the factor II occurs, and finally, fibrinogen is transformed into fibrin. In general, the strength or weakness, that is, the normality or abnormality, of the blood coagulation reaction through this pathway is judged by measuring a “prothrombin time (PT).”
The other pathway is referred to as an intrinsic coagulation, through which the coagulation factor XII is activated by contacting the surface of a solid phase having a negative charge and then activates the factor XI, the activated factor XI in turn activates the factor IX, and further, the activated factor IX activates the factor X with collaborative action of calcium ions and the factor VIII, then, the activation of the factor V and the factor II occurs, and finally, fibrinogen is transformed into fibrin. In general, the strength or weakness, that is, the normality or abnormality, of the blood coagulation reaction through this pathway is judged by measuring an “activated partial thromboplastine time (APTT),” a “partial thromboplastine time (PTT).”
In addition, at the final stage of the coagulation reaction, fibrinogen is required to be transformed into fibrin, whereby the coagulation completes.
As described above, the blood coagulation is a multiple-stage reaction, and thus, when abnormality occurs with the reaction pathways, unstable behavior may be expressed. For example, the reaction falls in such a state as if the reaction apparently stops temporarily in the middle of the reaction (an optical change is not observed), or alternatively, a gradual optical change is observed immediately after the blood coagulation reagent is introduced into plasma. Thus there are cases in which the reaction curve as shown in FIG. 1 is not always produced.
As an example, in the case where the coagulation time is measured based on an optical change amount with respect to high fibrinogen samples collected from heparin-administered patients, APTT sometimes tends to be extremely short. It is considered that such samples exhibit a two-bump reaction (the blood coagulation curve has two increase phases) due to a coagulation reaction caused by an extrinsic sthenia state as shown in FIG. 2: The optical change amount of the samples gradually increases with an elapse of time from the initial stage of the reaction, and then the optical change amount is larger than that of a normal coagulation reaction (second stage). As a result of such behavior different from usual, an incorrect coagulation time is considered to be computed.